Redundant External Storage Virtualization Computer System

1. A computer system comprising: a host entity for issuing IO requests; a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second external storage virtualization controller coupled to the host entity; and a set of at least one physical storage device for providing storage to the computer system, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the other storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein in the redundant storage virtualization controller pair, each of the storage virtualization controllers further comprises: a central processing circuitry for performing the IO operations in response to IO requests of said host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller coupled to said at least one physical storage device through said point-to-point serial-signal interconnect.

2. The redundant storage virtualization computer system of claim 1 wherein said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

3. The storage virtualization computer system of one of claims 1 and 2 wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in the same said IO device interconnect controller.

4. The storage virtualization computer system of one of claims 1 and 2 wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in different said IO device interconnect controllers.

5. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; wherein for each of at least one of the said physical storage devices, the redundant storage virtualization subsystem further comprises an access control switch coupled between said physical storage device and the redundant storage virtualization controller pair for selectively switching the connection of the said physical storage device to the redundant SVC pair between the first and the second storage virtualization controller; and wherein at least one said PSD together with said access control switch is installed in a canister removably attached to the redundant storage virtualization subsystem.

6. The redundant storage virtualization subsystem of claim 5 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

7. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; wherein for each of at least one of the said physical storage devices, the redundant storage virtualization subsystem further comprises an access control switch coupled between said physical storage device and the redundant storage virtualization controller pair for selectively switching the connection of the said physical storage device to the redundant SVC pair between the first and the second storage virtualization controller; and wherein said access control switch coupled between a said physical storage device and the redundant storage virtualization controller pair selectively allows patching through of the serial signal of the said physical storage device to and from the first SVC when in a first patching state of said access control switch and to and from the second SVC when in a second patching state of said access control switch.

8. The redundant storage virtualization subsystem of claim 7 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

9. The redundant storage virtualization subsystem of one of claims 7 and 8 , wherein an access ownership arbitration mechanism is provided between said SVC pair and said access control switch to control the patching state of said access control switch.

10. The redundant storage virtualization subsystem of claim 9 , wherein said access ownership arbitration mechanism comprises a pair of access request signal lines coupled between said SVC pair, said first SVC being active on a first of said access request signal line pair and passive on a second of said access request signal line pair; said second SVC being active on said second and passive on said first of said access request signal line pair; and said SVC pair each being capable of issuing an access request signal on its own said-active access request signal line, and reading a requesting state on its own said passive access request signal line and identifying a change of said requesting state since previous reading on its own said passive access request signal line.

11. The redundant storage virtualization subsystem of claim 9 , wherein said access ownership arbitration mechanism includes an access ownership detecting mechanism to determine if access ownership is possessed by a said SVC.

12. The redundant storage virtualization subsystem of claim 9 , wherein said access ownership arbitration mechanism includes an access ownership granting mechanism to grant access ownership when said access ownership is requested by a said SVC.

13. The redundant storage virtualization subsystem of claim 9 , wherein said access ownership arbitration mechanism comprises an access ownership arbitration circuit (AOAC) coupled to said first and second SVCs and said access control switch, and wherein if said first SVC issues a first access ownership request signal received by said AOAC, access ownership will be granted to said first SVC when said second SVC does not already possess the access ownership, and if said second SVC issues a second access ownership request signal received by said AOAC, access ownership will be granted to said second SVC when said first SVC does not already possess the access ownership.

14. The redundant storage virtualization subsystem of claim 13 , further comprises an access ownership determining mechanism whereby when said first and said second SVC concurrently issue said first and second access ownership request signals to said AOAC, access ownership will he granted to a predetermined one of said SVC pair.

15. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization ion controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVG pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; wherein for each of at least one of the said physical storage devices, the redundant storage virtualization subsystem further comprises an access control switch coupled between said physical storage device and the redundant storage virtualization controller pair for selectively switching the connection of the said physical storage device to the redundant SVC pair between the first and the second storage virtualization controller; and further comprising a cooperating mechanism for the redundant SVC pair to cooperatively control a patching state of said access control switch; a monitoring mechanism for each SVC of said SVC pair to monitor status of the other SVC of said SVC pair; and, a state control mechanism for each SVC of said SVC pair to forcibly take complete control of said access control switch independent of the state the other SVC of said SVC pair.

16. The redundant storage virtualization subsystem of claim 15 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

17. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein in the redundant storage virtualization controller pair, each of the storage virtualization controllers further comprises: a central processing circuitry for performing IO operations in response to IO requests of said host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller coupled to at least one physical storage device through a point-to-point serial-signal interconnect.

18. The redundant storage virtualization subsystem of claim 17 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

19. The redundant storage virtualization subsystem of one of claims 17 and 18 wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in the same said IO device interconnect controller.

20. The redundant storage virtualization subsystem of one of claims 17 and 18 wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in different said IO device interconnect controllers.

21. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein a logical media unit that is presented to said host entity through a first said host-side IO device interconnect port is also redundantly presented through a second said host-side IO device interconnect port.

22. The redundant storage virtualization subsystem of claim 21 , wherein the first said host-side IO device interconnect port and the second said host-side IO device interconnect port are IO device interconnect ports of the same one SVC in the redundant SVC pair.

23. The redundant storage virtualization subsystem of claim 21 , wherein the first said host-side IO device interconnect port is an IO device interconnect port of one SVC in the redundant SVC pair and the second said host-side IO device interconnect port is an IO device interconnect port of the other SVC in the redundant SVC pair.

24. The redundant storage virtualization subsystem of claim 21 , wherein the first said host-side IO device interconnect port and the second said host-side IO device interconnect port are coupled to the same host-side IO device interconnect.

25. The redundant storage virtualization subsystem of claim 24 , wherein the first said host-side IO device interconnect port and the second said host-side IO device interconnect port are coupled to the said same host-side IO device interconnect through a switch circuit.

26. The redundant storage virtualization subsystem of claim 21 , wherein the first said host-side IO device interconnect port and the second said host-side IO device interconnect port are each coupled to a different host-side IO device interconnect.

27. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is Fibre Channel supporting point-to-point connectivity in target mode.

28. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is Fibre Channel supporting public loop connectivity in target mode.

29. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is Fibre Channel supporting private loop connectivity in target mode.

30. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is parallel SCSI operating in target mode.

31. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is ethernet supporting the iSCSI protocol operating in target mode.

32. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is Serial-Attached SCSI (SAS) operating in target mode.

33. The redundant storage virtualization subsystem of one of claims 17 and 18 , wherein at least one said host-side IO device interconnect port is Serial ATA operating in target mode.

34. A redundant storage virtualization subsystem for, providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein an inter-controller communication channel is provided between the two SVCs in said redundant SVC pair for communicating state synchronization information.

35. The redundant storage virtualization subsystem of claim 34 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

36. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is an existing IO device interconnect, whereby inter-controller communication exchange is multiplexed with IO requests and associated data.

37. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is a dedicated channel the primary function thereof is to exchange said state synchronization information.

38. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is Fibre Channel.

39. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is Serial ATA.

40. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is Parallel SCSI.

41. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is Ethernet.

42. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is Serial-Attached SCSI (SAS).

43. The redundant storage virtualization subsystem of one of claims 34 and 35 , wherein said inter-controller communication channel is I2C.

44. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein said redundant SVC pair can perform IO request rerouting function.

45. The redundant storage virtualization subsystem of claim 44 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

46. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein said redundant SVC pair can perform PSD access ownership transfer function.

47. The redundant storage virtualization subsystem of claim 46 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

48. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein at least one member SVC of said redundant SVC pair includes at least one expansion port for coupling to a second set of at least one PSD through a multiple-device device-side IO device interconnect.

49. The redundant storage virtualization subsystem of claim 48 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

50. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein members of a set of at least one said expansion port are mutually coupled together and to the said second set of at least one PSD through a switch circuit.

51. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein members of a set of at least one said expansion port are mutually coupled together and to the said second set of at least one PSD directly without intervening circuitry.

52. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein a set of at least two said expansion ports form a redundant expansion pert set for mutually performing IO request rerouting function whereby IO requests normally delivered to a PSD through a first member port of said redundant expansion port set may be rerouted through a second member port of said redundant expansion port set.

53. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein a member of said second set of at least one PSD has a pair of redundant ports with a member port of said redundant port pair being coupled to a set of at least one said expansion port.

54. The redundant storage virtualization subsystem of claim 53 , wherein IO request rerouting function can be performed through said redundant ports of said member of said second set of at least one PSD whereby IO requests normally delivered to a PSD through a first member port of said redundant port pair may be rerouted to said PSD through a second member port of said redundant port pair.

55. The redundant storage virtualization subsystem of claim 54 , wherein a set of at least two said expansion ports form a redundant expansion port set for mutually performing IO request rerouting function whereby IO requests normally delivered to a PSD through a first member port of said redundant expansion port set may be rerouted through a second member port of said redundant expansion port set.

56. The redundant storage virtualization subsystem of claim 53 , wherein each member port in the said PSD redundant port pair is coupled to a different set of at least one expansion port.

57. The redundant storage virtualization subsystem of claim 53 , wherein said member port of redundant PSD port pair and said set of at least one said expansion port are mutually coupled together through a switch circuit.

58. The redundant storage virtualization subsystem of claim 57 , wherein said set of at least one expansion port comprises a first and a second expansion port subset forming a pair of complementary subsets with at least one member expansion port per subset.

59. The redundant storage virtualization subsystem of claim 58 , wherein one of the interconnect signal line switching mechanisms implemented by said switch circuit is the coupling of said first subset of the said complementary subset pair to a first member port of said PSD redundant port pair and coupling of said second subset of the said complementary subset pair to a second member port of said PSD redundant port pair.

60. The redundant storage virtualization subsystem of claim 58 , wherein one of the interconnect signal line switching mechanisms implemented by said switch circuit is the coupling of both subsets of the said complementary subset pair to a first member port of said PSD redundant port pair.

61. The redundant storage virtualization subsystem of claim 58 , wherein one of the interconnect signal line switching mechanisms implemented by said switch circuit is the coupling of said first subset of the said complementary subset pair to a first member port of said PSI) redundant port pair.

62. The redundant storage virtualization subsystem of claim 58 , wherein said switch circuit implements an interconnect signal line switching mechanism that supports all of the following arrangements: (1) coupling of said first subset of the said complementary subset pair to a first member port of said PSO redundant port pair and coupling of said second subset of the said complementary subset pair to a second member port of said PSD redundant port pair; (2) coupling of both subsets of the said complementary subset pair to said first member port of said PSI) redundant port pair; (3) coupling of both subsets of the said complementary subset pair to said second member port of said PSO redundant port pair; (4) coupling of said first subset of the said complementary subset pair to said first member port of said PSO redundant port pair; (5) coupling of said second subset of the said complementary subset pair to said second member port of said PSD redundant port pair; (6) coupling of said second subset of the said complementary subset pair to said first member port of said PSD redundant part pair; and, (7) coupling of said first subset of the said complementary subset pair to said second member port of said PSD redundant port pair.

63. The redundant storage virtualization subsystem of claim 53 , wherein said member port of redundant PSD port pair and said set of at least one said expansion port are directly coupled together without intervening circuitry.

64. The redundant storage virtualization subsystem of claim 53 , wherein a member SVC of the redundant SVC pair further comprises at least two said expansion ports forming a redundant expansion port set.

65. The redundant storage virtualization subsystem of claim 64 , wherein a first and a second member port in the said redundant expansion port set are each coupled to a different one of member ports in redundant PSD port pair of a member PSD of said second set of at least one PSD.

66. The redundant storage virtualization subsystem of claim 64 , wherein a first and a second member port in the said redundant expansion port set are both coupled to the same one of member ports in redundant PSD port pair of a member PSD of said second set of at least one PSD.

67. The redundant storage virtualization subsystem of claim 66 , wherein said first and said second member port are directly connected to the same one of member ports in redundant PSD port pair of a member of said second set of at least one PSD without intervening circuitry.

68. The redundant storage virtualization subsystem of claim 53 comprising: a first expansion port set comprising at least one said expansion port on the first SVC in the redundant SVC pair; a second expansion port set comprising at least one said expansion port on the second SVC in the redundant SVC pair; wherein said first expansion port set and said second expansion port set together form a redundant expansion port set pair.

69. The redundant storage virtualization subsystem of claim 68 wherein said first expansion port set and said second expansion port set are each coupled to a different one of member ports in redundant PSD port pair of each PSD of said second set of at least one PSD.

70. The redundant storage virtualization subsystem of claim 68 , wherein said first expansion port set and said second expansion port set are both coupled to the same one of member ports in redundant PSD port pair of each PSD of said second set of at least one PSD.

71. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein at least one said expansion port is Fibre Channel.

72. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein at least one said expansion port is Parallel SCSI.

73. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein at least one said expansion port is Serial ATA.

74. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein at least one said expansion port is Ethernet.

75. The redundant storage virtualization subsystem of one of claims 48 and 49 , wherein at least one said expansion port is Serial-Attached SCSI (SAS).

76. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the other storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein in the redundant storage virtualiztion controller pair, each of the storage virtualization controllers further comprises: a central processing circuitry for performing IO operations in respone to IO request of said host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO devie interconnect controller coupled to at least one physical storage device through said point-to-point serial-signal interconnect; and wherein said PSD is a SATA PSD.

77. The redundant storage virtualization subsystem of claim 76 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

78. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the other alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; wherein in the redundant storage virtualization controller pair, each of the storage virtualization controllers further comprises: a central processing circuitry for performing IO operations in response to IO request of said host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller coupled to at least one physical storage device through said point-to-point serial-signal interconnects; and wherein said PSD is a PATA PSD.

79. The redundant storage virtualization subsystem of claim 78 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

80. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein each SVC in said redundant SVC pair includes a state-defining circuit for forcing externally connected signal lines of alternate SVC in said redundant SVC pair to a predetermined state.

81. The redundant storage virtualization subsystem of claim 80 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

82. A redundant storage virtualization subsystem for providing storage to a host entity, comprising: a redundant external storage virtualization controller (SVC) pair for performing IO operations in response to IO requests issued by the host entity comprising a first and a second storage virtualization controller for coupling to the host entity; and a set of at least one physical storage device for providing storage to the host entity, with at least one member of said set of at least one physical storage device comprising a PSD coupled to the said redundant storage virtualization controller pair through a point-to-point serial signal interconnect; wherein when one storage virtualization controller in the said redundant SVC pair is not on line or goes off line after being on line, the alternate storage virtualization controller in the said redundant SVC pair will automatically take over the functionality originally performed by the said one storage virtualization controller in the redundant SVC pair; and wherein each SVC of said redundant SVC pair includes a self-killing circuit for forcing its own externally connected signal lines to a predetermined state.

83. The redundant storage virtualization subsystem of claim 82 wherein the said point-to-point serial signal interconnect is a Serial ATA IO device interconnect.

84. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in the same said IO device interconnect controller.

85. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein a said host-side IO device interconnect port and a said device-side IO device interconnect port are provided in different said IO device interconnect controllers.

86. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and further comprising a detection mechanism for detecting an off-line or failed state of said alternate storage virtualization controller.

87. The storage virtualization controller of claim 86 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

88. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said SVC includes a state-defining circuit for forcing externally connected signal lines of alternate SVC in said redundant SVC pair to a predetermined state.

89. The storage virtualization controller of claim 88 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

90. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said SVC includes a self-killing circuit for forcing its own externally connected signal lines to a predetermined state.

91. The storage virtualization controller of claim 90 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

92. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said functionality includes presenting and making available to the host entity accessible resources that were originally presented and made available by said alternate storage virtualization controller as well as accessible resources that were presented and made available by said storage virtualization controller itself.

93. The storage virtualization controller of claim 92 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

94. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein an access ownership arbitration mechanism is provided to determine which SVC in said SVC pair possesses access ownership.

95. The storage virtualization controller of claim 94 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

96. The storage virtualization controller of one of claims 94 and 95 , wherein said access ownership arbitration mechanism includes an access ownership detecting mechanism to determine if access ownership is possessed by said SVC.

97. The storage virtualization controller of one of claims 94 and 95 , wherein said access ownership arbitration mechanism includes an access ownership granting mechanism to grant access ownership when said access ownership is requested by a said SVC.

98. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and further comprising a cooperating mechanism for the redundant SVC pair to cooperatively control a patching state of an access control switch together with the alternate SVC; a monitoring mechanism for said SVC of said SVC pair to monitor status of the alternate SVC of said SVC pair; and, a state control mechanism for said SVC to forcibly lake complete control of said access control switch independent of the state the alternate SVC of said SVC pair.

99. The storage virtualization controller of claim 98 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

100. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein an inter-controller communication port is provided for communicating state synchronization information between the said SVC and the alternate SVC in said redundant SVC pair.

101. The storage virtualization controller of claim 100 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

102. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is an existing IO device interconnect port, whereby inter-controller communication exchange is multiplexed with IO requests and associated data.

103. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is a dedicated port the primary function thereof is to exchange said state synchronization information.

104. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is Fibre Channel.

105. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is Serial ATA.

106. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is Parallel SCSI.

107. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is Ethernet.

108. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is Serial-Attached SCSI (SAS).

109. The storage virtualization controller of one of claims 100 and 101 , wherein said inter-controller communication port is I2C.

110. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said SVC can perform IO request rerouting function.

111. The storage virtualization controller of claim 110 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

112. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said SVC can perform PSD access ownership transfer function.

113. The storage virtualization controller of claim 112 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

114. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein said SVC includes an expansion port for coupling to a second set of at least one PSD through multiple-device device-side IO device interconnects.

115. The storage virtualization controller of claim 114 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

116. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect part is Fibre Channel supporting point-to-point connectivity in target mode.

117. The storage virtualization controller of claim 116 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

118. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect port is Fibre Channel supporting public loop connectivity in target mode.

119. The storage virtualization controller of claim 118 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

120. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least. one said host-side IO device interconnect port is Fibre Channel supporting private loop connectivity in target mode.

121. The storage virtualization controller of claim 120 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

122. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect port is parallel SCSI operating in target mode.

123. The storage virtualization controller of claim 122 wherein the a said at least one device-side. IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

124. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect port is ethernet supporting the iSCSI protocol operating in target mode.

125. The storage virtualization controller of claim 124 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

126. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect port is Serial-Attached SCSI (SAS) operating in target mode.

127. The storage virtualization controller of claim 126 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.

128. An external storage virtualization controller for use in a redundant storage virtualization controller pair, comprising: a central processing circuitry for performing IO operations in response to IO requests of a host entity; at least one IO device interconnect controller coupled to said central processing circuitry; at least one host-side IO device interconnect port provided in a said at least one IO device interconnect controller for coupling to said host entity; and at least one device-side IO device interconnect port provided in a said at least one IO device interconnect controller for performing point-to-point serial signal transmission with at least one physical storage devices; wherein the said external storage virtualization controller will automatically take over the functionality originally performed by the alternate external storage virtualization controller in the said redundant storage virtualization controller pair when said alternate external storage virtualization controller is not on line or goes off line after being on line; and wherein at least one said host-side IO device interconnect port is Serial ATA operating in target mode.

129. The storage virtualization controller of claim 128 wherein the a said at least one device-side IO device interconnect port comprises a Serial ATA interconnect port for connecting to a said physical storage device through a Serial ATA IO device interconnect.